Naturally occurring and synthetic smectite clays such as bentonite, montmorillonite, hectorite, sapoite, nontronite, etc. are generally comprised of layers which may be visualized as a "sandwich" or platelet containing two outer sheets of silicon tetrahedra and an inner or central octahedral sheets of a hydrous metal oxide, such as alumina or magnesia octahedra. These platelets are stacked one upon the other to yield a clay particle. Normally this arrangement yields a repeating structure about every ten angstroms to give a material with low surface area. Smectites can be classified into two categories, dioctahedral and trioctahedral, the differences being the number of octahedral sites in the central sheet which are occupied. This, in turn, is related to the valence of the cation in the central sheet, with the dioctahedral smectites having central cations which are trivalent and substituents which are divalent, whereas the trioctahedral smectites have divalent central cations with monovalent substitutents.
It is known that increased permanent porosity could be introduced into smectite clay minerals by separating these platelets further, by as much as 30 to 40 angstroms, by intercalation with various polar molecules such as water, ethylene glycol and various amines which function as molecular props or pillars, separating the platelets and preventing the layers from collapsing to van der Waals contact. Thus, a variety of organic materials could be adsorbed on the exposed intracrystal surfaces. However, the interlayered clays thus prepared were not suitable for general adsorbent and catalytic applications because of the limited resistance to decomposition at high temperatures (maximum about 250.degree. C.) of the interlayer cations.
More recently, increased interest in "pillared" clay intercalates has resulted in work being done to develop classes of ions which would separate the platelets further and/or would exhibit thermal stability to about 500.degree. C. or greater. A variety of robust cations have been suggested for use to pillar smectite clays, including bicyclic amine cations, tris metal chelates, and polyoxocations. Small oxide aggregates have also been suggested as pillars. Such pillared smectites have formed materials useful as adsorbents, catalyst supports, filter medium or the like. For example, in U.S. Pat. No. 4,176,090, and U.S. Pat. No. 4,271,043, montmorillonite interlayered with polyoxocations of aluminum and zirconium have been shown to function as cracking catalysts for conversion of petroleum distillates to high-octane gasoline and diesel fuel with efficiencies comparable to that of commercial zeolite-based catalysts. The polyoxocation pillars are stable inorganic polymers of oxides of the metals formed by hydrolysis of metal salts which were impregnated into the open structure of the clay at the appropriate pH. Such stable, pillared smectite clay compositions have an interlayer spacing in the range of 14 to 20 angstroms. Also, in U.S. Pat. Nos. 4,216,188 and 4,238,364 are shown pillared or cross-linked smectites such as montmorillonite formed with aluminum or chromium hydroxide pillars having uniform interlayer distances (basal spacing) in the range of up to about 20 angstroms.
However, it has been found that there are limitations in the pore sizes that can be achieved in such pillared smectite compositions and in the molecular size of organic materials with which they can be used. It would, therefore, be highly desirable to prepare clay materials having thermal stability with an expanded pore size which would permit admission and free diffusion of large hydrocarbon and other molecules in the intracrystalline pore system.
It is, therefore, a primary object of this invention to provide a method for providing smectite clay compositions having lammellar and delaminated association of the layers of clay.
Another object of this invention is to provide a new and improved smectite clay composition of high temperature stability with expanded pore size that would permit admission and free diffusion of large hydrocarbon and other molecules.
Still another object of this invention is to provide a method for producing new and improved smectite clay compositions of high temperature stability and with expanded pore size that would permit admission and free diffusion of large hydrocarbon and other molecules.
Another object of the invention is to provide porous expanded clay materials having intercalated structures between the interlayers of clay.
Still another object of the invention is to provide a method for producing smectite clay compositions which are useful as catalyst supports, adsorbents, filtering bed media and the like.
These and still further objects of the invention will become readily apparent to one skilled in the art from the following detailed description, specific Examples and drawings.